The selective removal of hydrogen sulfide from carbon dioxide containing gas streams by absorption is an important, albeit highly specialized, segment of industrial technology. Hydrogen sulfide is especially useful in the manufacture of elemental sulfur, but in order to use it effectively, the hydrogen sulfide should be made available in a molar ratio of carbon dioxide to hydrogen sulfide approaching and preferably no greater than about 6. In some applications such as, for example, in a Claus plant, the molar ratio should be no greater than about 3. Since the usual molar ratios found in typical feedstocks such as natural gas and synthetic natural gas, are in the neighborhood of about 5 to about 140, reduction of these ratios is usually a prerequisite to the use of hydrogen sulfide so obtained. This means that the selectivity of any commercially acceptable selective absorption process must be such that a high proportion of carbon dioxide passes through the absorber unabsorbed while a small proportion of the hydrogen sulfide follows that same path. The most advantageous process from a competitive point of view is, of course, the one which is most selective and has apparatus and energy requirements equal to or less than other commercial processes.
A principal object of this invention, therefore, is to provide a process for the selective removal of hydrogen sulfide from carbon dioxide containing gas streams whereby the selectivity is such that molar ratios of carbon dioxide to hydrogen sulfide approaching about 6, and preferably about 3, or less are realized for the overall process while maintaining other process requirements at levels equal to or better than competitive processes.
Other objects and advantages of the present invention will become apparent from the following description and disclosure.